1. Field of the Invention
The present invention relates to a construction for transmitting the displacement of a piezoelectric element to a mating member.
2. Description of the Related Art
A stacked piezoelectric element, which is constituted by ceramic piezoelectric plates which are stacked in a direction in which the piezoelectric plates are displaced when voltage is applied thereto via internal electrodes, is known. The piezoelectric plates are displaced when voltage is applied to respective piezoelectric plates via the associated internal electrodes, and the sum of the respective displacements becomes the overall displacement of the stacked piezoelectric element.
In employing the displacement of the stacked piezoelectric element, the displacement thereof is transmitted, to a mating member which requires it, via a displacement transmission construction.
The displacement transmission construction is required to have a performance for transmitting the displacement of the piezoelectric element to the mating member without any loss.
In order to minimize the loss of displacement to be transmitted, there may be a case where between the displacement transmitting construction and the mating member to which the displacement of the piezoelectric element is transmitted by the construction contact surfaces of both the displacement transmitting construction side and the mating member side, are formed flat. Since transmission of a displacement between flat surfaces reduces Hertz stress, a loss in transmitting the displacement can be minimized.
However, it is extremely difficult to machine either of the displacement transmitting construction and the mating member such that their contact surfaces become a smooth plane. Since there exist a number of minute irregularities on the contact surfaces, in many cases the contact condition between the displacement transmitting construction and the mating member does not become a plane contact but becomes a partial contact.
In addition, since the stacked piezoelectric element is made of ceramic and is therefore fragile, it is desired that end faces of the stacked piezoelectric element in the displacement direction are in parallel with each other. In the event that the both end faces are not in parallel with each other, loads applied to the stacked piezoelectric element from the end faces become unbalanced, or unbalanced loads are exerted on the stacked piezoelectric element, and therefore, there may be a risk that the piezoelectric plates fracture or are damaged.
Additionally, a displacement transmitting construction such as disclosed in Japanese Unexamined Patent Publication No. 8-275563 is known.
This displacement transmitting construction has a conical concave surface as a contact surface, and there is provided a member between the displacement transmitting construction and the mating member which has a hemispherical convex surface for receiving the concave surface.
When an unbalanced load is exerted on the displacement transmitting construction due to a bending force relative to a direction which is in parallel with the displacement direction of the piezoelectric element, the hemispherical convex surface rotates appropriately to prevent the transmission of the unbalanced load to the piezoelectric element side. Thus, the displacement transmitting construction is characterized in that the piezoelectric element is prevented from being fractured or damaged. However, as the displacement of the piezoelectric element is absorbed by the rotation or the collapse of the contact surface, or the displacement of the piezoelectric element is absorbed by a slight deformation in the plane contact surface of the member which has the hemispherical convex surface, this displacement transmitting construction is not desirable.
In addition, even in the event that the displacement transmitting construction, and a member which is brought into a direct contact therewith, are brought into contact with each other both at the convex surfaces, it is difficult to prevent the occurrence of the aforesaid slight deformation. Additionally, there may be a risk that the protruding end of the convex surface collapses due to the displacement of the piezoelectric element, the dead weight of the piezoelectric element itself, or loads applied to the piezoelectric element, to thereby absorb the displacement of the piezoelectric element, causing a loss in transmitting the displacement.
The present invention was made in view of the above situations, and an object thereof is to provide a construction for transmitting the displacement of a piezoelectric element which can be disposed between a stacked piezoelectric element and a mating member to which a displacement is transmitted without any extra member being interposed therebetween, which can minimize a loss associated with the transmission of a displacement and which can make it difficult to apply an unbalanced load to the stacked piezoelectric element.
With a view to attaining the object, according to the invention, there is provided a construction for transmitting the displacement of a piezoelectric element which is constructed in such a manner as to transmit, to a mating member, a displacement generated in a stacked piezoelectric element when the stacked piezoelectric element is energized to be driven and which comprises a piston member which is in direct contact with the piezoelectric element and is disposed at one end face of the piezoelectric element in a displacement direction thereof and a distal-end plate portion which has a receiving face adapted to be brought into direct contact with a distal-end face of the piston member in the displacement direction of the piezoelectric element and which is adapted to be brought into direct contact with a mating member at a displacement transmitting face thereof which is situated on an opposite side to the receiving face, the construction for transmitting the displacement of a piezoelectric element being characterized in that both end faces of the piezoelectric element in the displacement direction thereof are maintained substantially in parallel with each other, in that a contact configuration between the distal-end face of the piston member and the receiving face of the distal-end plate portion is in annual and linear conditions, and in that the piezoelectric element, the piston member and the distal-end plate portion are constructed to be substantially stationary relative to directions except for the displacement direction of the piezoelectric element at least while the piezoelectric element is being driven.
In the invention, the piezoelectric element is brought into direct contact with the displacement transmitting construction, which is, in turn, brought into direct contact with the mating member. Consequently, it is possible to reduce Hertz stress generated at a contact portion where different members are brought into contact with each other and a loss which occurs when a displacement is absorbed by a deformation of the respective members.
In addition, since the end faces of the piezoelectric element in the displacement direction thereof is maintained substantially in parallel with each other, it is difficult to exert an unbalanced stress and, therefore, it is difficult for stress to be concentrated on a specific portion of the piezoelectric element. Thus, the piezoelectric element can be prevented from being damaged.
Additionally, as the contact configuration between the distal-end face of the piston member and the receiving face of the distal-end plate portion is in annular and linear contact conditions, when compared with a case where curved surfaces are brought into point contact with each other, the displacement transmitting construction and the distal-end plate portion are allowed to be in contact with each other in a stable condition, and since they contact with each other linearly, the displacement transmitting construction and the distal-end plate portion deform less than when they are in point contact with each other, thereby making it possible to transmit the displacement of the piezoelectric element to the mating member with a limited loss.
Thus, according to the invention, it is possible to provide a construction, for transmitting the displacement of a piezoelectric element, which can be disposed between a stacked piezoelectric element and a mating member to which a displacement is transmitted without any extra member being interposed therebetween, which can minimize a loss associated with the transmission of a displacement and which can make difficult the application of an unbalanced load to the stacked piezoelectric element.
The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings.